1. Field of the Invention
The invention relates generally to a bio-oil having reduced mineral content, and more particularly to process for preparing such bio-oils.
2. Description of the Related Art
Depending on its origin, biomass may contain significant amounts of minerals, generally referred to as ash. In academic papers, experiments have been described in which biomass was subjected to a wash treatment prior to prolific conversion. These experiments show that minerals present in biomass have an effect on both the conversion yield and product mix of biomass conversion processes.
Biomass conversion processes generally produce gaseous, liquid, and solid products. The liquid products comprise an aqueous phase and an oil phase. The oil phase is generally referred to as bio-oil. It is generally assumed that minerals present in biomass end up in the aqueous phase of the biomass conversion products. Bio-oil is known to be unstable, which is generally ascribed to high oxygen content of the bio oil. No attention is being given to the possible role of minerals contamination of the bio-oil as a contributing factor to the instability of bio-oil.
U.S. Pat. No. 6,022,419 to Torget et al. discloses a multi-step process for acid hydrolysis of lignocellulose. The first step, which is optional, is designed to solubilize the most easily dissolved components, such as some lignin, extractives, and any protein. For this optional step, a hot aqueous medium is used having a temperature in the range of from 100 to 160° C. and a pH in the range of from 1 to 5. The extractives are not separated from the biomass.
U.S. Pat. No. 6,419,788 to Wingerson discloses a process for separating cellulose from other constituents of the ligno-cellulosic biomass. The focus of the disclosed process is on the removal of lignin. Extractives are removed together with lignin and residual hemicellulose. The process aims at producing a relatively clean cellulose free of lignin.
US published patent application 2008/029233 to Wingerson discloses a countercurrent process for separating cellulose fibers from other constituents of a lignocellulosic biomass. The first wash liquids can include water, or a solution of water and a mineral acid for hemicellulose hydrolysis.
These prior art processes comprised removal of extractives in the context of producing a substantially lignin free cellulose product. For the production of bio-oil it is desirable to leave the lignin in the feedstock, as it contains an important portion of the energy presence in the biomass.
Thus, there is a particular need for a process aimed at minimizing the mineral content of a bio-oil, and the bio-oil produced by such a process.